Insulating film and electronic device

Abstract

An insulating film includes a first barrier layer, a well layer provided on the first barrier layer, a second barrier layer provided on the well layer. The first barrier layer consists of a material having a first bandgap and a first relative permittivity. The well layer consists of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity. The second barrier layer consists of a material having a third bandgap larger than the second bandgap and having a third relative perminivity smaller than second relative permittivity. Each of the first and second barrier layers has a thickness not smaller than 2.5 angstroms, and 2.5>(d 1/ε1 +d 2/ε2 ) is satisfied where d 1 and d 2 (angstrom) are the thicknesses of the first and second barrier layers, respectively, ε 1 is the first relative permittivity, and ε 2 is the third permittivity.

1. An insulating film comprising:
 a first barrier layer consisting of a material having a first bandgap and a first relative permittivity; 
 a well layer provided on the first barrier layer, consisting of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity, discrete energy levels being formed in the well layer by a quantum effect; and 
 a second barrier layer provided on the well layer, consisting of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity, 
 each of the first and second barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied:
   2.5>( d 1/ε1+ d 2/ε2) 
 
 where d 1  (angstrom) is the thickness of the first barrier layer, ε 1  is the relative permittivity of the first barrier layer, d 2  (angstrom) is the thickness of the second barrier layer and ε 2  is the third permittivity of the second barrier layer, 
 wherein the first bandgap is a bandgap of SiO 2 . 
 
     
     
       2. An insulating film comprising:
 a first barrier layer consisting of a material having a first bandgap and a first relative permittivity; 
 a well layer provided on the first barrier layer, consisting of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity, discrete energy levels being formed in the well layer by a quantum effect; and 
 a second barrier layer provided on the well layer, consisting of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity, 
 each of the first and second barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied:
   2.5>( d 1/ε1+ d 2/ε2) 
 
 where d 1  (angstrom) is the thickness of the first barrier layer, ε 1  is the relative permittivity of the first barrier layer d 2  (angstrom) is the thickness of the second barrier layer and ε 2  is the third permittivity of the second barrier layer, 
 wherein 
 energy levels of conduction bands of the first and second barrier layers are higher than an energy level of a conduction band of silicon by 1.0 electron volt or more, and 
 energy levels of valence bands of the first and second barrier layers are lower than an energy level of a valence band of silicon by 1.0 electron volt or more. 
 
     
     
       3. An insulating film comprising:
 a first barrier layer consisting of a material having a first band gap and a first relative permiflivity; 
 a well layer provided on the first barrier layer, consisting of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity, discrete energy levels being formed in the well layer by a quantum effect; and 
 a second barrier layer provided on the well layer, consisting of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity, 
 each of the first and second barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied:
   2.5>( d 1/ε1+ d 2/ε2) 
 
 where d 1  (angstrom) is the thickness of the first barrier layer, ε 1  is the relative permittivity of the first barrier layer, d 2  (angstrom) is the thickness of the second barrier layer and ε 2  is the third permittivity of the second barrier layer, 
 wherein the barrier layers each consists of a material selected from the group consisting of (Ba,Sr,Ca)O, SiO 2 , Si 3 N 4 , SiON, Al 2 O 3 , Hf-silicate, nitride of Hf-silicate, Zr-silicate, nitride of Zr-silicate, Ti-silicate, nitride of Ti-silicate and MgAl 2 O 4 , (Ba,Sr,Ca)F. 
 
     
     
       4. An insulating film comprising:
 a first barrier layer consisting of a material having a first bandgap and a first relative permittivity, having a conduction band whose energy level is higher than an energy level of a conduction band of silicon by 0.5 electron volts or more and having a valence band whose energy level is lower than an energy level of a valence band of silicon by 0.5 electron volts or more; 
 a well layer provided on the first barrier layer, consisting of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity, and having a bandgap smaller than a bandgap of SiO 2  and having a relative permittivity larger than a relative permittivity of SiO 2 , and a thickness of the well layer being not larger than 5 angstroms, discrete energy levels being formed in the well layer by a quantum effect; and 
 a second barrier layer provided on the well layer, consisting of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity, having a conduction band whose energy level is higher than an energy level of a conduction band of silicon by 0.5 electron volts or more and having a valence band whose energy level is lower than an energy level of a valence band of silicon by 0.5 electron volts or more. 
 each of the first and second barrier layers having a thickness not smaller than 2.5 angstroms, and the following condition being satisfied:
   2.5>( d 1/ε1+ d 2/ε2) 
 
 where d 1  (angstrom) is the thickness of the first barrier layer, ε 1  is the relative permittivity of the first barrier layer, d 2  (angstrom) is the thickness of the second barrier layer and ε 2  is the third permittivity of the second barrier layer. 
 
     
     
       5. The insulating film according to  claim 4 , wherein the first and second barrier layers each have a thickness not smaller than 3.5 angstroms. 
     
     
       6. The insulating film according to  claim 4 , wherein the well layer consists of a material selected from the group consisting of (Ba,Sr,Ca)TiO 3 , (Ba,Sr,Ca)(Ti,Zr)O 3 , Pb(Zr,Ti)O 3 , Ta 2 O 5 , CeO 2 , HfO 2 , HfON, ZrO 2 , ZrON, TiO 2 , Hf-silicate, HfSiON, Zr-silicate, ZrSiON, Ti-silicate, Y 2 O 3 , LaAlO 3 , Ga 2 O 3 , La 2 O 3  and Al 2 O 3 . 
     
     
       7. The insulating film according to  claim 4 , wherein
 the barrier layers each consists of a material selected from the group consisting of (Ba,Sr,Ca)O, SiO 2 , Si 3 N 4 , SiON, Al 2 O 3 , Hf-silicate, nitride of Hf-silicate, Zr-silicate, nitride of Zr-silicate, Ti-silicate, nitride of Ti-silicate and MgAl 2 O 4 , (Ba,Sr,Ca)F, and 
 the well layer consists of a material selected from the group consisting of (Ba,Sr,Ca)TiO 3 , (Ba,Sr,Ca)(Ti,Zr)O 3 , Pb(Zr,Ti)O 3 , Ta 2 O 5 , CeO 2 , HfO 2 , HfON, ZrO 2 , ZrON, TiO 2 , Hf-silicate, HfSiON, Zr-silicate, ZrSiON, Ti-silicate, Y 2 O 3 , LaAlO 3 , Ga 2 O 3 , La 2 O 3  and Al 2 O 3 .